While there seems to be a general perception that any given heat exchanger structure may be utilized interchangeably for any of a variety of heat exchange operations, for example, as an oil cooler, as a radiator, as a condenser, as an evaporator, etc., this is frequently not the case, particularly where one of the heat exchange fluids is undergoing a phase change during the heat exchange operation as, for example, from liquid to vapor or the reverse. Simply stated, the change of phase, in many instances, considerably alters the mechanics of the heat exchange operation; and this is particularly true in the case of evaporators used in refrigeration systems.
In such a system, one heat exchange fluid will be directed toward the evaporator principally in the liquid phase. In some instances, it may be entirely in the liquid phase while in others, it may be in a mixed phase of both liquid and vapor. In any event, the refrigerant is passed through an expansion valve or a capillary into a low pressure area which includes the evaporator itself. The refrigerant downstream of the expansion valve or capillary will initially be in the mixed phase. That is, made up of both refrigerant liquid and refrigerant vapor.
Because the refrigerant is flowing within the system, it will have kinetic energy which in turn will be related to its mass. And, of course, for a given volume of refrigerant in the liquid phase versus the same volume of refrigerant in the vapor phase, the kinetic energy, and thus momentum, will be substantially greater because of the much higher density of the liquid phase material.
As a consequence, as the mixed phase refrigerant enters a manifold or a header in the evaporator which is provided for distributing refrigerant to several different flow paths through the evaporator as is typical, the momentum of the liquid phase component of the incoming refrigerant often tends to cause the refrigerant to flow rapidly down a large portion or even all of the length of the manifold to essentially pool or puddle at one end thereof. Consequently, flow paths connected to the manifold near the inlet frequently receive principally vapor phase refrigerant while those more remote from the inlet receive principally liquid phase refrigerant. Since vapor phase refrigerant has already absorbed the latent heat of vaporization, those flow paths conducting a principally vapor phase refrigerant cannot absorb all of the heat that they are capable of absorbing whereas those receiving principally liquid phase refrigerant, because of thermal conductivity constraints in the evaporator design, cannot absorb all of the heat that the liquid phase refrigerant flowing therethrough is capable of absorbing.
The same factors influence vaporization in each pass of a multiple pass evaporator. Additionally, outlet resistance may also cause a maldistribution of refrigerant among the flow paths.
The obvious result is poor efficiency of operation of the evaporator.
The present invention is directed to overcoming one or more of the above problems.